1. Field of the Invention
The present invention is directed to separating methods, separators used in such methods, apparatuses used in such methods, and, in certain particular aspects, to methods for separating clay materials, often referred to as “gumbo,” from drilling fluids.
2. Description of Related Art
The separation of solid particles from fluid streams by passing a fluid through a screening device having perforations sized so that solid particles are retained on the screen surface instead of passing through it is well-known in the prior art. Some fluid streams contain additional materials that cause solid particles to agglomerate or to adhere to each other or to a screen surface, resulting in bridging of the screen openings and blinding of the screen. Such a problem is frequently encountered in the drilling of wells during which a drilling fluid or “mud” is circulated into the wellbore.
Drilling mud is continuously circulated between the bore hole and the surface to remove drilled cuttings, also called drilled solids, from the drill bit during drilling operations. Cuttings are carried in the drilling fluid to the surface where they are separated from the fluid which is then recirculated to the drilling operation. The drilling mud is kept as clean and free of contamination by cuttings and foreign materials as possible. Drilling mud is typically cleaned by several types of equipment sequentially, including vibratory screening machines commonly referred to as “shale shakers”.
During the drilling of a wellbore material of a gummy clay formation can make the separation of drilling cuttings from the drilling mud by screening operations very difficult. Gummy hydrated clay or “gumbo” adheres to the surfaces of screens and screening machines causing a buildup which can blind the screens so that the drilling mud, rather than passing through the screen where it can be recirculated, passes over and off the end of the screen where it is unrecoverable. This hydrated clay or gumbo has non-Newtonian rheological properties which contribute to these problems; e.g., it generally displays the properties of a fluid that has an increase in its viscosity with time under the influence of a suddenly applied constant shear stress and it tends to form into a cohesive mass or “gumbo patty” on screening equipment that resists separation by vibratory screening equipment because it does not readily pass through the screen openings and can not be conveyed off the screen to a waste stream because its viscosity increases as additional energy is applied by the screening machine in an attempt to transport it off the screen. This increase in viscosity results in the gumbo becoming more resistant to conveying as more energy is applied to transport it off the screen and the gumbo then tends to reduce the capacity of mud cleaning equipment to separate cuttings from drilling mud by clogging the screens and reducing their open area.
As more gumbo is removed from drilling mud during drilling, it can accumulate in screening equipment, thus the screening equipment's ability to clean the drilling mud and, in some circumstances, such an accumulation can reduce the effectiveness of or prevents the cleaning of the recirculating mud, reducing the drilling rate and increase drilling costs.
Contamination of drilling fluid can increase drilling costs significantly and reducing the capacity of mud cleaning equipment can limit the rate at which a well can be drilled, increasing the time required for drilling and increasing drilling expense. Drilling mud with gumbo in it can increase the viscosity of the mud, reducing the drilling rate and increasing costs.
Some prior art methods for dealing with gumbo during drilling have employed chemical additives to change the properties of the drilling mud, which adds cost to an already substantial drilling expense. Some prior art mechanical efforts, such as increasing the vibrational amplitude of separator devices and adding various types of water sprays have been ineffective when the gumbo forms a new steady state gumbo patty at the new operating conditions. Some attempted solutions to the gumbo problem have included applying specialized coatings to screens, e.g., as described in U.S. Pat. No. 3,963,605 (incorporated fully herein for all purposes), but such coatings can add cost to the screening equipment, and may be quickly worn off the screens by abrasive cuttings.
U.S. Pat. No. 5,921,399, incorporated fully herein for all purposes, discloses a gumbo separator comprising a vessel which is roughly rectangular, having side plates, a back plate, and an open base upon which the vessel rests. The vessel has a fluid inlet through which a fluid solution passes, a fluid outlet through which cleaned fluid passes, and a solid discharge outlet through which separated solids pass to disposal. The gumbo separator has a continuous, inclined, moving screen belt riding on and supported by a perforated backing plate to remove solids from the fluid solution and, in one embodiment, to clean expensive drilling mud. The screen belt and perforated backing plate are constructed of materials which in combination have low sliding friction and are wear resistant. A variable speed drive assembly moves the belt at a rate for removing gummy materials from drilling fluid before it can clog equipment used to remove drilling cuttings from the mud. The gumbo separator can be activated only when gumbo is encountered.
Accordingly, there remains a need in the art for apparatus to effectively remove gumbo from recirculating drilling mud. There has long been a need, recognized by the present inventor, for an efficient and effective method to separate hydrated clay from drilling fluid.